Yes, it's better. Yes, it matters. Vacuum tubes are human, ya know, and it never hurts to warm them up and cool them off. In fact, one of the design goals of the transistor was to have a device that didn't have the long warmup/cooloff cycle of tubes. Look up the early tube computers' specs sometime: they each had a crew of many people whose only job was going around replacing the 1000's of tubes required to amplify the signal to the required level.